The present invention relates to an improved stonework crusher, and more particularly relates to improvements in a shape memory alloy type crusher used for crushing stoneworks such as big stones, rocks and building structures made of stones or concretes.
Such a shape memory alloy (SMA) type stonework crusher is highly appreciated in the field of stonework construction because of its easy handling and relatively quick operation when compared with crushing via water expansion. Its safety in handling and operation is also highly welcomed in practice in particular in comparison with explosion type crushing which often endangers workers and ambient inhabitants and, as a consequence, is limited in application, due to its dangerous nature.
Some SMA type crushers are proposed in Japanese Patent Openings Sho. No. 60-115794 and Sho No. 61-169600. In construction of the crushers of these earlier proposals, a heating element situated at the center of a crusher is surrounded by a cylindrical shell made of SMA. In operation, the crusher is inserted into a bore or a groove naturally or artificially formed in a stonework and the cylindrical shell is heated by the heating element so that thermal deformation of the shell should apply a crush force to the walls of the bore or the groove to crush the stonework.
In the case of such a SMA type crusher, the cylindrical shell expands in all radial directions during the thermal deformation. In other words, the cylindrical shell expands into directions not contributing to enlargement of the bore or the groove and, as a consequence, the thermal deformation of the cylindrical shell cannot be fully utilized for generation of the crush force. In addition, thermal deformation of the cylindrical shell enlarges the space between the central heating element and the surrounding shell, thereby lowering efficiency in heat transmission to the shell. In particular when two or more stonework crushers are used in combination, variation in thermal deformation caused by such enlarged space between the heating element and the shell tends to impair concerted action of these crushers, thereby leading to unsuccessful crushing of the stonework.
In an attempt to measure the magnitude of a force necessary for successfully crushing a stonework, a series of experimental tests were conducted using rectangular concrete columns of various square sections. The height of each column was 200mm and the side length of the square was changed. A SMA rod of 10mm diameter and 20mm length was sued as a crusher. The rod had a built-in curvature about the middle of its length. After insertion into a vertical bore of 10mm diameter and 120mm. depth formed in the top face of the concrete column, the rod was heated to restore its built-in curvature. As a result of the test, it was confirmed that the concrete columns could be successfully crushed only when the side length of the square section was 1/3 or smaller than the length of the SMA rod. This results indicates the fact that, in order to crush a big stonework, crusher rods have to be arranged in a bore or groove in the stonework at an interval of about 2 times as large as the diameter of the rod whilst necessitating great deal of labour and time. From these experimental data, it is well understood that a large force is necessary to crush a stonework.
For these reasons, most of the conventional SMA-type crushers have not been widely used in practice. Even when used, it is inevitably accompanied with increased labour, time and cost.